Lenticular lens sheet and projection screen

ABSTRACT

A high contrast a lenticular lens sheet that improves the brightness of an image and the angle of visibility. The width A, between the lens elements on a light-emission side and a side wall of a black stripe portion is made to be 15 μm or less. P represents the pitch of the lens element and H represents the width of the black stripe portion as viewed n a cross section perpendicular to the lens element, the difference F in height between the black stripe portion and the lens element is set to have a range that is expressed by the inequality: 0.098 P≦F≦(P-H)/2 tan(π/3). Simultaneously, the width B as measured from an apex portion of the black stripe portion in regard to a colored portion on a side wall of the black stripe portion is set to have a range that is expressed by the inequality: 0.30 F≦B≦0.89 F.

TECHNICAL FIELD

The present invention relates to a lenticular lens that is usable for arear projection television, etc., and a projection screen that uses thelenticular lens.

BACKGROUND ART

For a rear projection television, there is used a projection screenwherein a lenticular lens is superposed on the light-emission side of aFresnel lens. At the boundary portion of the lens elements provided onthe light-emission side (the viewer side) of the lenticular lens sheet,the so-called black stripe portion that has been colored black isprovided in parallel with the lens element for enhancing the contrast(e.g. see Japanese Patent Application Laid-Open No. 10-254064 andJapanese Patent Application Laid-Open No. 2000-284366). As the policyfor improving the contrast, attempts have also been made to color thelenticular lens sheet itself.

However, in the conventional lenticular lens sheet, depending on theexternal-light conditions, it happened that the reflection of theexternal light by the lens decreased the contrast of the image and thisobstructed the viewer's visual recognition of it. The method for solvingthe lenticular lens sheet itself has the drawback that, although thecontrast is improved, the utilization efficiency of the image lightdecreases; and as a result the brightness of the image as well as theangle of visibility decreases.

DISCLOSURE OF THE INVENTION

Thereupon, the present invention has an object to provide a lenticularlens sheet and a projection screen capable of providing a high contrastand improving the brightness of the image as well as the angle ofvisibility and to provide a projection screen.

In a first aspect of the present invention, there is provided alenticular lens sheet comprising a light-emission surface provided withlens elements, a black strip portion being provided at each borderbetween the lens elements, wherein each lens element and a correspondingside wall of the black stripe portion is in contact with each other, oreach lens element is connected to the side wall via a portion ofconnection that, when viewed in a cross section perpendicular to thelens element, has a width A which is greater than 0 and which is equalto or less than 15 μm.

According to this aspect of the invention, it is intended to decreasethe amount of the reflected light which, after an external light hasbeen incident upon the lenticular lens sheet from the light-emissionsurface side, goes out from the border between the lens element and theblack stripe portion and from the neighborhood of that border, toward aviewer who is situated in front of the screen. Thereby, it is possibleto sufficiently improve the contrast. It is to be noted that a statewhere each lens element and a side wall of the black stripe portion arein mutual contact with each other means the one where the end edge ofthe lens element and the side wall of the black stripe portion arecontinuous without the intermediary of a portion of connection.

In a second aspect of the present invention, there is provided alenticular lens sheet comprising a light-emission surface provided withlens elements, a black strip portion being provided at each borderbetween the lens elements, wherein when it is assumed that P representsthe pitch of the lens element; and H represents a width of the blackstripe portion when viewed in a cross section perpendicular to the lenselement, the difference F in height between the black stripe portion andthe lens element is set to have a range that is expressed by theinequality:0.098 P≦F≦(P−H)/2 tan(π/3)and wherein the width B as measured from an apex portion of the blackstripe portion in regard to a colored portion on a side wall of theblack stripe portion is set to have a range that is expressed by theinequality:0.30 F≦B≦0.89 F

According to this aspect of the invention, it is possible to suppressthe increase in the opening area for the incidence of the external lighton the light-emission surface side. And it is possible, whilesuppressing that increase, to provide a sufficient colored area in theblack stripe portion and to sufficiently ensure the degree of shieldability for the light-incidence and light-emission of the externallight. Thereby, it is possible to enhance the contrast sufficiently.Also, it is possible to ensure the angle of visibility of 60 degrees ormore. In addition, it is also possible to prevent the coloring onto thelens element on the light-emission surface side and thereby prevent theoccurrence of black-dot defects on the projection screen.

In a third aspect of the present invention, there is provided alenticular lens sheet comprising a light-emission surface provided withlens elements, a black strip portion being provided at each borderbetween the lens elements, wherein the light reflection property of acolored portion of the black stripe portion is set so that theall-light-ray reflectance thereof is equal to or less than 4.6% and thatthe diffuse reflectance thereof is equal to or less than 1.5%.

According to this aspect of the invention, the reflected lightcomponent, which is included in reflected light components to bereflected upon the surface of the black stripe portion in response toincidence of the external light from the light-emission surface side ofthe lenticular lens sheet, and which is directed toward the watcher infront of the projection screen, is decreased, so that the contrast isenhanced.

As described above, according to the first to the third aspects of thepresent invention, the contrast is improved by setting the dimensions ofthe respective portions and the reflectance thereof to specifiedconditions. Therefore, even if performing no coloring with respect tothe lens sheet, it is possible to sufficiently enhance the contrast andto enhance the utilization efficiency of the image light to therebyprovide a bright image. In addition, it is also possible to enhance theangle of visibility. Especially, in case that the lenticular lens sheethas been constructed with the technical features described in the abovefirst to third aspects combined with one another, it is possible toremarkably enhance the contrast, the utilization efficiency of the imagelight, and the angle of visibility. Therefore, this is preferable.

Further aspect of the present invention, there is provided a projectionscreen equipped with any one of the above described lenticular lenssheets according to the present invention. According to this aspect ofinvention, it is possible to provide, utilizing the characteristic ofthe above-described lenticular lens sheet, the projection screen thecontrast of that is high and is excellent in terms of the brightness ofthe image and the angle of visibility.

Incidentally, the cross section perpendicular to the lens element in thepresent invention is referred to as a “section” that can be obtained bysectioning the lenticular lens sheet along with both of the directionparallel to a direction in which the lens elements are arranged and thedirection of the optical axis of each lens element. Also, theall-light-ray reflectance of the black stripe portion means a value thathas been obtained from the measurement that is in accordance with K7105of Japanese Industrial Standard (JIS). And the diffuse reflectance meansa value that has been obtained from the measurement of the amount ofscattered light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a lenticular lens sheet to which thepresent invention is applied;

FIGS. 2A and 2B are views each illustrating a main part of thelight-emission surface side of the lenticular lens sheet of FIGS. 1, 2Abeing a sectional view that intersects the lens element at a right anglewith respect thereto and 2B being a side view taken from thearrow-IIb-indicated direction;

FIG. 3 is a view illustrating an example of light paths each includingan external light incident upon the light-emission surface side of thelenticular lens sheet and a reflected light thereof;

FIG. 4 is a view illustrating the angle of visibility regarding the lenselement on the light-emission surface side;

FIG. 5 is a sectional view of a projection screen;

FIG. 6 is a diagram showing a table of results according to the example1;

FIG. 7 is a diagram showing a table of results according to the example2; and

FIG. 8 is a diagram showing a table of results according to the example3.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates an embodiment of a lenticular lens sheet to which thepresent invention is applied. The lenticular lens sheet (hereinafter mayaccording to the cases be abbreviated as “the lens sheet”) isconstructed of a transparent resin. On the light-incidence surface side(the downside of the illustration) thereof are unidirectionally arrangedat equal pitches a number of lens elements 2 . . . 2 each of that hasbeen constructed as a substantially semi-cylindrical convex lens. On theother hand, on the light-emission surface side (the upside of theillustration) of the lens sheet 1 are arranged at equal pitches in thesame direction a number of lens elements 3 . . . 3 each of that has beenconstructed as a substantially semi-cylindrical convex lens similarly.The optical-axis direction of the lens element 2 and that of the lenselement 3 coincide with each other.

At a border of the lens elements 3 . . . 3 of the light-emission surfaceside is formed a black stripe portion 4 . . . 4 in parallel with thelens element 3. The black stripe portion 4 has an apex portion 5 formedinto a planar configuration that perpendicularly intersects thethickness direction of the lens sheet (the vertical direction of FIG. 1)1, and a pair of side walls 6, 6 each of that perpendicularly intersectsthe apex portion 5. The apex portion 5 more protrudes than the lenselement 3. The whole surface of the apex portion 5 and upper endportions of the paired side walls 6 are colored black with a black-colorink that has an external-light absorption property, and are therebyconstructed as a colored portion 7. It is to be noted that in FIG. 1 thecolored portion 7 is indicated with hatching. Although in FIG. 1 thecolored portion 7 of one side wall 6 is only illustrated, the same istrue of the colored portion 7 of the opposite side.

FIG. 2A illustrates a section that intersects the lens element 3 at aright angle with respect thereto on the light-emission surface side ofthe lens sheet 1. As apparent from this figure, at the joining portionbetween the lens elements 3 and the black stripe portions 4, there areformed portions of connection 8 . . . 8 each of that has a substantiallycircular-arc like sectional configuration. It is to be noted that theportion of connection 8 is not limited to a circular-arc section. If itis a portion that has a sectional configuration that is different fromthat of any one of the lens element 3 and the black stripe portion 4,that portion is included in that portion of connection 8. Also, theborder portion between the portion of connection 8 indicated in FIG. 2Aby the mark “black circle” and the lens element 3 is a point at whichthe curvature that is to be imparted to the lens element 3 ends. Theborder portion between the side wall 6 and the portion of connection 8is a point at which the flat plane of the side wall 6 ends.

In the lens sheet 1 of the above-described construction, in thisembodiment, the physical properties, such as the dimensions, of therespective portions are set as follows.

(1) Regarding the Portion of Connection 8

The width A in the cross section of the lens element 3 has been set soas to be greater than 0 and equal to or smaller than 15 μm. The reasonfor this is as follows.

FIG. 3 illustrates a state in which the external light that has reachedthe lens sheet 1 in the light-emission surface side is reflected. Asindicated by doted lines in FIG. 3, it is possible that the externallight which has entered the interior of the lens sheet 1 from the lenselement 3 will be reflected within the lens sheet 1 and go out from thelens element 3. This external light which emits from the lens element 3is added to the image light which emits from the lens element 3. As aresult of this, the contrast decreases. In addition, it is considered asbeing general that the viewer or watcher looks at the screen from thefront (the thickness direction) of the lens sheet 1. Therefore, theexternal light (that is indicated in bold lines in FIG. 3) which emitsstraightforward in the thickness direction of the lens sheet 1 has thegreatest adverse effect upon the decrease in the contrast. According tothe present inventors' studies, it has been confirmed that, from theportion of connection 8, the reflected light relatively more frequentlyemits especially in the thickness direction of the lens sheet 1. And ithas also been confirmed that, the more narrowed the width A of theportion of connection 8, the more remarkably enhanced the contrast thatis obtained when the lens sheet 1 has been looked at from the frontthereof. The smaller the width A of the connection portion 8, the morepreferable it is. It has been confirmed that by setting the width A to avalue of 15 μm or less the contrast can be definitely improved.

(2) Regarding the Difference F in Height Between the Black StripePortion 4 and the Lens Element 3 and the Width B of the Colored Portion7 of the Side Wall

The difference F in height between the black stripe portion 4 and thelens element 3 has been set to the following range relative to the pitchP of the lens element 3 and the width H in the cross-section of theblack stripe portion 4.0.098 P≦F≦(P−H)/2 tan(π/3)

As the difference F in height is greater, it is possible to makenarrower the area through which the external light enters the lenselement 3. However, when that height F exceeds the value (P−H)/2 tan(π/3), as illustrated in FIG. 4 the angle of visibility of the diffusionimage light that emits from the lens element 3 on the light-emissionside becomes 60° C. or less. Therefore, the angle of visibility becomesshort, with the result that the screen is unsuitable as the projectionscreen. On the other hand, when the difference F in height becomessmaller than 0.098 P, the area of the opening portion through which theexternal light enters the lens sheet 1 from the light-emission surfaceside becomes excessively large. In addition, the area of the coloredportion 7 of the black stripe portion 4 becomes short. As a result ofthese, the improvement effect of the contrast cannot be admitted.

Next, the width B of the colored portion 7 of the side wall 6 of theblack stripe portion 4 (provided, however, that the width B is a valuethat has been obtained by being measured from the apex portion 5 in thethickness direction of the lens sheet 1) has been set to the range thatis expressed by the following inequality:0.30 F≦B≦0.89 F

In case the width B of the colored portion 7 is smaller than 0.30 F, thearea for shielding the incidence and emission of the external light bymeans of the side wall 6 is insufficient, with the result that theimprovement effect of the contrast is not obtained. Further, when thewidth B exceeds 0.89 F, black-coloring of the colored portion 7 becomeslikely to have an effect upon the lens element 3 during themanufacturing process thereof. As a result of this, black-color pointsdefects unsuitably occur on the projection screen.

(3) All-Light-Ray Reflectance and Diffuse Reflectance of the ColoredPortion 7

The all-light-ray reflectance of the black stripe portion 4 has been setto 4.6% or less, which the diffuse reflectance has been set to 1.5% orless. Either in case the all-light-ray reflectance exceeds 4.6% or incase the diffuse reflectance exceeds 1.5%, the reflected lightcomponents directed from the black stripe portion 4 toward the viewerside non-ignorably increase. As a result of this, the improvement effectof the contrast is lost.

The lens sheet 1 that has been constructed as above is disposed on thelight emission side of the Fresnel lens 9 as illustrated in FIG. 5. Theprojection screen 10 is basically constructed with the combined use ofthe Fresnel lens 9 and the lenticular lens sheet 1. However, otherconstituent elements such as a protection screen for preventing flaws orstain may further be superposed on the projection screen 10.

EXAMPLES (1) Example 1

For examining a proper range for the width A of the connection portion 8between the lens element 3 of the light-emission side and the side wall6 of the black stripe portion 4, a lenticular lens sheet meeting theconditions of the following table 1 was manufactured. Thereby, thecontrast of the resulting screen was evaluated. The evaluated resultsare concurrently shown as the table 1 in FIG. 6.

From the results of the examinations made as above, it has beenconfirmed that the width A of the connection portion that is effectivefor the enhancement of the contrast was 15 μm or less.

(2) Example 2

For examining a proper range for the difference F in height between theblack stripe portion 4 and the lens element 3 as well as for the width Bof the colored portion 7 on the side wall 6, a lenticular lens sheetmeeting the conditions of the following table 2 was manufactured.Thereby, the contrast was evaluated. The evaluated results areconcurrently shown as the table 2 in FIG. 7.

From the results of the examinations made as above, the following wereconfirmed. Namely, the range for the difference F in height that iseffective for the enhancement of the contrast is as follows,0.098 P≦F≦(P−H)/2 tan(π/3)while the range for the width B is as follows.0.30 F≦B≦0.89 F

It is to be noted that the evaluations in the table 2 are the ones thathave been made using the sample 2 as a reference and in that the effectof the contrast as measured from that reference has been relativelyevaluated. Accordingly, the mark “x” in the table 2 does not indicatethat the absolute evaluation of the contrast is unsuitable. The samples7 to 9 are each intended to examine the height F. This is for thepurpose of finding out the lower limit value thereof. To this end, thewidth B of the colored portion of the side wall in each of the samples 7to 9 was set to have a lower limit value of 30 μm when the height F was100 μm (sample 9).

Also, the upper limit value (P−H)/2 tan (π/3) of the difference F inheight is the one that is geometrically determined so as to satisfy thecondition that the angle θ (see FIG. 4) becomes 60 degrees. In case theangle θ of visibility is under 60 degrees, it is confirmed that theresulting lenticular lens sheet is unsuitable as the lenticular lenssheet. Also, regarding the upper limit of the width B of 0.89 F, when itexceeds 0.89 F, the following has been confirmed. Namely, that the inkto be applied to the side wall 6 of the black stripe 4 is adhered ontothe lens element 3 as well, and that the frequency at which black colordot defects occur on the lens sheet 1 becomes high.

(3) Example 3

For examining a proper range for the light reflection property regardingthe colored portion 7 of the black stripe 4, a lenticular lens sheetmeeting the conditions described in the following table 3 wasmanufactured. And the contrast of that sheet was evaluated. Theevaluated results are concurrently shown as the table 3 in FIG B.

From the results of the examinations made as above, it has turned outthat, as the light reflection property of the colored portion 7effective for the enhancement of the contrast, the all-light-rayreflectance is 4.6% or less while the diffuse reflectance is 1.5% orless. It is to be noted that the evaluations in the table 3 are the onesthat have been made using the sample 10 as a reference and in that theeffect of the contrast as measured from that reference has beenrelatively evaluated. Accordingly, the mark “x” in the table 3 does notindicate that the absolute evaluation of the contrast is unsuitable.

The present invention is not limited to the above-described embodimentand examples and permits various changes or modifications to be madewithout departing from the technical idea described in the scope of theclaims. For example, in the above-described embodiment, there has beendescribed the form of construction wherein the connection portion 8 thewidth A of that is greater than 0 exists between the lens element 3 andthe side wall 6 of the black stripe portion 4. However, it may bearranged that if possible with the connection portion 8 being madenon-existent, i.e. with the width A being made to be 0 the lens element3 and the side wall 6 be in contact with each other.

INDUSTRIAL APPLICABILITY

As has been explained above, according to the present invention,settings have been made, as described above, with regard to thefollowing factors. The width of the border portion between the lenselement on the light-emission surface side of the lenticular lens sheetand the black stripe portion; the difference in height between the blackstripe portion and the lens element; the width of the colored portion inthe side wall of the black stripe portion; and the light reflectionproperty of the black stripe portion. Therefore, it is possible toprovide a lenticular lens sheet and projection screen the contrast ofthat is high and that can improve the brightness of the image as well asthe angle of visibility.

1. A lenticular lens sheet comprising a light-emission surface providedwith lens elements, a black strip portion being provided at each borderbetween the lens elements, wherein each lens element and a correspondingside wall of the black stripe portion is in contact with each other,wherein when it is assumed that P represents the pitch of the lenselement; and H represents the width of the black stripe portion whenviewed in a cross section perpendicular to the lens element, thedifference F in height between the black stripe portion and the lenselement is set to have a range that is expressed by the inequality:0.098 P≦F≦(P−H)/2 tan(π/3) and wherein the width B as measured from anapex portion of the black stripe portion in regard to a colored portionon a side wall of the black stripe portion is set to have a range thatis expressed by the inequality:0.30 F≦B≦0.89 F.
 2. A projection screen which is equipped with thelenticular lens sheet according to claim
 1. 3. A lenticular lens sheetcomprising a light-emission surface provided with lens elements, a blackstrip portion being provided at each border between the lens elements,wherein each lens element and a corresponding side wall of the blackstripe portion is in contact with each other, wherein the lightreflection property of a colored portion of the black stripe portion isset so that the all-light-ray reflectance thereof is equal to or lessthan 4.6% end the diffuse reflectance thereof is equal to or less than1.5%.
 4. A projection screen which is equipped with the lenticular lenssheet according to claim
 3. 5. A lenticular lens sheet comprising alight-emission surface provided with lens elements, a black stripportion being provided at each border between the lens elements, whereinwhen it is assumed that P represents the pitch of the lens element; andH represents a width of the black stripe portion when viewed In a crosssection perpendicular to the lens element, the difference F in heightbetween the black stripe portion and the lens element is set to have arange that is expressed by the inequality:0.098 P≦F≦(P−H)/2 tan(π/3) and wherein the width B as measured from anapex portion of the black stripe portion in regard to a colored portionon a side wall of the black stripe portion is set to have a range thatis expressed by the inequality:0.30 F≦B≦0.89 F.
 6. A lenticular lens sheet comprising a light-emissionsurface provided with lens elements, a black strip portion beingprovided at each border between the lens elements, wherein the lightreflection property of a colored portion of the black stripe portion isset so that the all-light-ray reflectance thereof is equal to or lessthan 4.6% and that the diffuse reflectance thereof is equal to or lessthan 1.5%.